The present invention relates to a disk player, particularly relates to a disk player for playing a disk carrying a video signal recording thereon.
For example, in an optical disk player, if the relative angle between an optical axis of an information reading light beam and a recording surface of a disk deviates from a right angle, information will leak from an adjacent track, thereby producing so-called cross-talk phenomenon. Deviation from a right angle may be caused by-various factors, such as, for example, a phenomenon that a disk becomes umbrella-like due to secular distortion, a phenomenon that the disk rotation axis is tilted due to the change in shape of a deck portion of a player, and so on. These causes of the problem occur after the shipment of the products, so that it has been impossible to prevent the cross-talk phenomenon from occurring.
Where an information recording disk (hereinafter simply abbreviated as "disk") has a warp due to secular distortion or the like, the information recording surface of the disk is tilted relative to the optical axis of an information detecting light beam emitted from an optical pickup so as to narrow the track pitch between adjacent recording tracks. Assuming that the diameter of a beam spot on the information recording surface is constant, therefore, a track is apt to be affected by pit information of an adjacent track, resulting in increased cross talk. The influence of this cross-talk appears as a noise component in a video signal reproduced from the disk, resulting in deterioration of the picture. In order to improve such deterioration in performance, there has been provided a so-called tilt-servo which is arranged so that the tilt of the optical axis of the information detecting light beam relative to the information recording surface of the disk is detected and the tilt of the pickup is adjusted to keep the optical axis of the light beam always perpendicular to the information recording surface.
As shown in FIG. 1, there is provided a servo system to electrically detect cross-talk in question to always accurately keep the orthogonal relation between a light beam axis and a disk, thereby reducing the cross-talk phenomenon. In FIG. 3, a disk 1 is driven to rotate by a spindle motor 2 and the information recorded on the disk 1 is read out by a pickup 3. The pickup 3 includes a laser diode, an objective lens, a focus actuator, a tracking actuator, a photo detector, a tilt sensor and so on. The output of the photo detector of the pickup 3 is fed to a video signal reproducing/processing circuit 4 as well as an audio signal reproducing/processing circuit 5, and at the same time is fed also to a focus servo circuit (not-shown) as well as a tracking servo circuit (not-shown). These focus and tracking servo circuits drive the focus and tracking actuators in the pickup 3 to thereby control laser light emitted from the laser diode in the pickup 3 so that laser light is focused onto the recording surface of the disk 1 thereby forming an information detecting light spot positioned on a track formed on the recording surface of the spot 1.
The tilt sensor in the pickup 3 is constituted, for example, by a light emission means arranged to emit light directed toward the recording surface, and a pair of light receiving elements arranged to receive light reflected from the recording surface and disposed on a predetermined line perpendicular to the recording track in a plane perpendicular to the optical axis of the emitted light so as to be symmetrical with each other with respect to the light emission means. The output of the tilt sensor in the pickup 3 is fed to a tilt detecting circuit 6. The tilt detecting circuit 6 is, for example, constituted by a differential amplifier arranged to receive at its positive and negative inputs the respective outputs of a pair of light receiving elements constituting the tile sensor. This tilt detecting circuit 6 generates a tilt detection signal corresponding to the tilt of the recording surface of the disk 1 relative to a reference plane depending on a relative angle between the optical axis of the light beam emitted from the pickup 3 and the recording surface of the disk 1. The position of the pickup 3, and the tilt detection signal is fed to a motor in a tilt adjusting mechanism 7 as a driving signal for the motor. The tilt adjusting mechanism 7 is arranged to rotate the pickup 3 in accordance with the tilt detection signal about an axis extending substantially in the direction parallel to the recording surface of the disk 1 and perpendicular to the radial direction of the disk 1 to thereby correct the tilt of recording surface of the disk 1. The tilt sensor, the tilt detecting circuit 6 and the tilt adjusting mechanism 7 are disclosed in Japanese Utility Model Application No. 58-87555.
In the video signal reproducing/processing circuit 4, and FM signal having an instantaneous frequency which changes in accordance with a video signal is extracted from the output of the pickup 3 and fed to an FM modulator so that the video signal is reproduced. The reproduced video signal put out from the video signal reproducing/processing circuit 4 is fed to a video output terminal 9 after noise due to cross-talk and so on caused by the tilt of the disk 1 has been reduced by a noise reduction circuit 8.
In the audio signal reproducing/processing circuit 5, an EFM (Eight to Fourteen Modulation) signal is extracted from the output of the pickup 3 and fed to an EFM demodulator so that an audio signal is reproduced. The reproduced audio signal put out from the audio signal reproducing/processing circuit 5 is fed to an audio output terminal 11 after undesired components have been eliminated by a LPF (Low Pass Filter) 10.
FIGS. 2 and 3 show details of the tilt sensing and correction apparatus of FIG. 1. In FIG. 2, the optical pickup 3 includes an objective lens 40 for reading recorded information of a disk 1 which is driven to rotate by a spindle motor 2. The objective lens 40 is attached to an optics body 50 movable in the direction of its optical axis, and driven by a focus actuator not-shown. The optics body 50 is attached to a slider base 60 so as to be rotatable about a pivotal point 0 positioned on an optical axis A--A' of the objective lens 40. An adjusting mechanism 7 constituted by a tilt motor M (shown in FIG. 3), and reduction mechanism and so on rotates the optics body 50 round the slider base 60 so as to adjust the tilt of the optical axis A--A' of the objective lens 40 relative to the information recording surface. The slider base 60 is arranged to be movable along a not-shown guide rail in the radial direction B--B' of the disk 1, and driven by a driving mechanism (not shown), such as a slider motor, a reduction gear and so on.
In a plane that includes the optical axis A--A' of the objective lens 40 and that is perpendicular to the moving direction of the slider base 60, a tilt sensor 80 is provided in the vicinity of the objective lens 40 in order to detect the tilt angle of the disk 1 relative to the optical axis A--A'. This tilt sensor 80 is, as shown in FIG. 3, constituted by a light emission element 90 and two light receiving elements 100a and 100b, so that a light beam emitted from the light emission element 90 is reflected on the information recording surface of the disk 1 and the light thus reflected is received by the light receiving elements 100a and 100b. A difference between the respective intensities of light received by the light receiving elements 100a and 100b is obtained by a differential amplifier 110, and a signal representing this difference is fed through a driving amplifier 12 to a tilt motor 13 in an adjusting mechanism 7 (shown in FIG. 2), as the information related to the tilt of the disk 1 relative to the optical axis A--A'.
In such an arrangement, when the slider base 60 moves from a position &lt;a&gt; to a position &lt;b&gt; in FIG. 2 and arrives at a tilted portion of an outer circumferential portion of the disk 1, the adjusting mechanism 7 is driven in response to a driving signal based on the output of the tilt sensor 80 so that the optics body 50 is rotated in the clockwise direction in FIG. 2 about the pivotal point 0 so as to carry out a tilt servo to make the optical axis A--A' perpendicular to the information recording surface of the disk 20.
In such a conventional disk player as described above with reference to FIGS. 1-3, the tilt of the recording surface of the disk 1 relative to the reference plane depending on the position of the pickup 3 is corrected by means of a mechanical system, and moreover the reduction of noise is performed by means of the noise reduction circuit 8. In this arrangement, however, there has been a problem that the structure of the arrangement is complicated and expensive. Moreover, since the tilt sensor 80 is mounted on the pickup 3, it becomes difficult to miniaturize the pickup 3. Accordingly, there has been a problem that the circuit arrangement is complicated and the production cost is high.